1. Field of the Invention
This invention relates to a thyristor for the low-loss triggering of short impulses, which is provided with an integrated auxiliary thyristor in order to improve the current rise time during turn-on, and an integrated diode in order to shorten the thyristor turn-off time.
2. Description of the Prior Art
It is one of the essential tasks for the follow-up development of thyristors to improve the thyristor's turning-on and turning-off properties. The installation of an auxiliary thyristor or amplifying gate between the portion of the p-base used as a gate and the adjacent border strip of the cathode emitter layer is a customary measure in order to improve the steepness of the current rise when turning-on. The application of a negative voltage to the gate during the turn-off interval is another known measure in order to shorten the thyristor turn-off time. In the art this is called a gate assisted turn-off (GATT).
The two measures are not independent of each other but the auxiliary thyristor arranged between the gate and the cathode emitter impairs the effect of the negative voltage at the gate on the cathode emitter when turning-off. In order to overcome this disadvantage, it is known to use an integrated diode which is connected in antiparallel to the auxiliary thyristor and short-circuits it when a negative voltage is applied to the gate. Corresponding investigations are described by J. Shimzu et al. in IEEE Transactions on Electron Devices, Vol. ED-23, August 76, Page 883. As has been shown in practice, also this measure has deficiencies. The diode contains an n.sup.+ -layer which injects electrons into the p-base when applying the negative voltage to the gate. These electrons can effect an uncontrolled ignition and possibly even the destruction of the thyristor when they get in sufficient quantities into the space charge zone induced by the blocking voltage which is rising again after the turning-off of the thyristor. In order to remove this deficiency, tests have been carried out to enlarge the distance of the n.sup.+ -p-junction of the diode from the space charge zone of the thyristor which means in practice that the n.sup.+ -layer of the diode is diffused less deeply into the p-zone than the n.sup.+ -layers of the emitters of the thyristor and of the auxiliary thyristor. The technology required for this purpose is rather complex and it has been shown in practice that, even with thyristors conceived in this fashion, the uncontrolled ignition during the gate assisted turn-off can only be avoided when the negative impulse at the gate is adjusted to the properties of the thyristor and its operating conditions.